Here is only one scenario other than an asteroid strike that could end the world as we know it in a matter of hours: nuclear war.

Until now, no one outside official circles has known exactly what would happen if a rogue state launched a nuclear missile at the Pentagon. Second by second and minute by minute, these are the real-life protocols that choreograph the end of civilization as we know it.

Decisions that affect hundreds of millions of lives need to be made within six minutes, based on partial information, in the knowledge that once launched, nothing is capable of halting the destruction.

Based on dozens of new interviews with military and civilian experts who have built the weapons, been privy to the response plans, and taken responsibility for crucial decisions, this is the only account of what a nuclear exchange would look like.